Traveling wave amplifier tube



Och--27, 1953 K. s. KNQL nF'AL mix-mm WAVE AMPLIFIER TUBE Filed Dec. 26, 1947 II I IN VEN TORS.

KORAELIS 5WIER KNOL ALBERT WINDERZZEL AGEVI Patented Oct. 27, 1953 2,657,328 TRAVELING WAVE AMPLIFIER TUBE Kornelis Swier Knol and Aldert van der Ziel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford,

Conn., as trustee Application December 26, 1947, Serial No. 794,051 In the Netherlands January 13, 1947 4 Claims. 1

For the amplification of waves of the order of magnitude of centimetres, it is known to use a tube comprising a helical conductor guiding the waves to be amplified, Whilst along the axis of the helix an electron beam is produced, the electrons of which exhibit a velocity chosen to be such with respect to the velocity of the waves in the direction of the axis of the helix that the electrons give oiT energy to the propagating waves so as to cause the latter to be amplified at the end of the helix.

The waves to be amplified are supplied to the end of the helix nearest to the electron beam, whilst the pitch of the helix and/or the diameter of the turns, as well as the voltages used for producing the electron-beam are chosen to be such that the velocity of propagation of the Waves measured along the axis of the helix is slightly lower than the mean velocity of the electrons of the beam. Under these conditions the electrons give off energy to the waves, so that the latter may be derived in amplified form from the end of the helix remote from the source of electrons.

In order to avoid stationary waves on the helix, the output end of the helix is required to be blocked by an impedance matched to the helix. However, since it is thus not possible completely to suppress reflections at the output end of the helix, it has also proved to be necessary for the electrical resistance of the helix to have a fairly high value. As a matter of course, this measure has a detrimental effect on the amplification to be obtained on account of losses occurring in the material of the resistance.

The invention is based on recognition of the fact that in this case the losses in the material of the resistance at the input end of the helix preponderate over the energy procured by the beam, so that here the amplitude of the wave is materially damped and this is detrimental not only to amplification but also to a favourable signal-to-noise ratio.

The object of the invention is to avoid stationary waves without involving heavy losses at the beginning of the helix itself.

According to the invention a plurality of turns at the beginning of the helix are made of conductive material, whereas the remaining part of the helix consists of turns consisting of material of poor conductivity.

In order that the invention may be clearly understood and readily carried into efiect, it will now be described more fully with reference to the accompanying drawing.

Referring to the sole figure of the drawing, reference numeral l designates the envelope of the tube and 2 designates a device known per se for producing an electron-beam, the electrons of which move along the axis of the tube and may impinge upon a counter-electrode 3. The tube furthermore comprises, concentrically with its axis, a helically-wound conductor which consists of two parts 6 and l merging into one another approximately at point 8. Part 6 consists in this case of turns of high conductivity for high-frequency currents, whereas part 1 consists of turns damping the high-frequency waves to a fairly considerable degree. The end of the helix nearest to the electron source 2 is connected to earth through an impedance 4, which has suppliedto it the oscillations to be amplified. The other end of the helix is likewise earthed through an impedance 5 which is matched to the surge impedance of the helix and from which the amplifled oscillations may be obtained.

Since the high-frequency currents flow substantially along the surface of the helix, the desired properties of the turns may, for example, be ensured by making the coil from material of poor conductivity and by covering the first turns with material of high conductivity, for example silver. Conversely, the whole of the helix may be manufactured from material of high conductivity and the last turns coated with material of poor conductivity.

In practice the helix may consist of wire of approximately 0.5 mm, thickness and the outer diameter of the turns may be about 6 mms. The helix may be wound with 5 turns per cm. and may consist, for example, of turns. The first 20 to 50 turns may be of conductive material and the remaining turns may be of material of low conductivity. The transition between the two portions may be gradual, although this is not always required. A tube constructed in this manner is adapted for amplifying waves of about 8 cms. of length. It is, otherwise, evident that the dimensions of the helix and the voltages required for producing the electron-beam are dependent on the desired amplification and on the wavelength of the oscillations to be amplified.

What we claim is:

1. In a traveling-wave electron beam tube for the amplification of high-frequency oscillations, the combination comprising a helical conductor for guiding oscillations, input means to supply the oscillations to be amplified to one end of said conductor, output means to extract the amplified oscillations from the other end of said conductor, means to generate an electron beam, and means to direct said beam along the axis of said helical conductor with a velocity which at any point thereon exceeds that of the traveling wave of said oscillations along the helical conductor as measured along said axis, said conductor having a conductivity at the output end portion thereof which is lower than the conductivity at the input end portion thereof such that the damping of the traveling wave is high at the output end portion relative to the input end portion.

2. In a traveling-wave electron beam tube for the amplification of high-frequency oscillations,

the combination comprising a helical conductor for guiding oscillations, input means to supply the oscillations to be amplified to one end of said conductor, output means to extract the amplified oscillations from the other end of said conductor, means to generate an electron beam, and means to direct said beam along the axis of said helical conductor with a velocity which at any point thereon exceeds that of the traveling Wave of said oscillations along the helical conductor as measured along the said axis, the turns of said conductor at the output end thereof having a conductivity which is lower than the conductivity of the turns of the conductor at the input end thereof such that the damping of the traveling wave is high at the output end relative to the input end.

, 3. In a traveling-wave electron beam tube for the amplification of high-frequency oscillations, the combination comprising a helical conductor for guiding oscillations, input means to supply the oscillations to be amplified to one end of said conductor, output means to extract the amplified oscillations from the other end of said conductor, means to generate an electron beam, and means to direct said beam along the axis of said helical conductor with a velocity which at any point thereon exceeds that of the travel .means to derive the amplified oscillations from 'the other end of said conductor, an electron- "beam gun-structure adjacent the input end of said helical conductor, and a collector electrode adjacent the output end of said helical conductor, said gun being arranged to direct the electron "beam along the axis of said helical conductor toward said collector electrode with a velocity which "at "any point thereon exceeds that of the traveling wave of said oscillations as measured along said axis, said helical conduc tor having a higher conductivity at the input end portion thereof than at the output end .por- .tion thereof .such that thedamping of the traveling wave is higher at the output end portion relative to that at the input end portion.

KORN-ELIS ,SWIER 'KNOL. ALDERT VAN DER ZIEL,

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,122,538 Potter July 5, 1938 2,283,126 Hae'fi Feb. 25, 1941 2,300,052 Lindenblad Oct. '27, 1942 2,413,608 Di Toro Dec. 31, 1946 2,541,843 Tiley Feb. 13, 1951 2,575,383 Field Nov. 20, 1951 2,602,148 Pierce 1 July 1, 1952 OTHER REFERENCES Article by J. R. Pierce, Bell Lab. Record, December 1946, pp. 439-442, inclusive. Copy in Division 54.. 

